The present invention relates generally to electronic ballasts and, more particularly, to disable self-oscillating electronic ballasts for fluorescent lamps.
Discharge lamps, such as fluorescent lamps, may implement a ballast to maintain a stable discharge current in the lamp. The ballast is placed in the lamp circuit to provide a high starting voltage to ignite the lamp followed by a current-limiting mode of operation. Conventional electronic ballasts accomplish this task through the use of active semiconductor switches and reactive passive components such as inductors and capacitors. More specifically, modern ballast circuits include a pair of serially connected switches, such as MOSFETs, which convert direct current into alternating current for supplying a resonant load circuit in which the gas discharge lamp is positioned.
In some applications, particularly integral compact fluorescent lamps (CFLs), the integration of the ballast with the lamp may demand small ballast size and low ballast cost to produce a viable product. One class of circuits that may meet these demands is the group of self-oscillating resonant ballasts, such as L-comp ballasts.
In some applications, it is further desirable to have the ability to control the brightness of the lamp. Controlled brightness may be desirable to attain energy savings or to appeal to personal lighting preferences, for example. The brightness of the lamp is controlled by controlling the lumen output in the lamp. Controlling the brightness of the lamp may be accomplished with self-oscillating ballasts. However, while high performance dimmable lamps may be attained using self-oscillating ballasts, conventional designs implement circuits which are substantially more complex and expensive compared to the non-dimmable circuits. Further, such designs may necessitate the use of an ASIC to be practical.
It may be desirable to implement a simple, low cost ballast circuit having a small size to provide a method for controlling the lumen output of the lamp driven by the ballast circuit.
In accordance with one aspect of the present technique, there is provided a ballast circuit comprising: a resonant load circuit comprising an input electrically coupled to a gas discharge lamp; and a resonant control circuit coupled to the input of the resonant load circuit and configured to convert a dc signal to an ac signal and to provide the ac signal to the input of the resonant load circuit, wherein the resonant control circuit comprises a variable resistor configured to adjust the switching frequency of the ballast circuit.
In accordance with another aspect of the present technique, there is provided a gas lamp comprising: one or more bulbs; a ballast circuit coupled to the one or more bulbs and comprising a resonant load circuit comprising an input electrically coupled to the one or more bulbs, and a resonant control circuit coupled to the input of the resonant load circuit and configured to convert a dc signal to an ac signal and to provide the ac signal to the input of the resonant load circuit, wherein the resonant control circuit comprises a variable resistor configured to adjust the switching frequency of the ballast circuit; an adjustable knob coupled to the variable resistor and configured to adjust the variable resistor; and a stem configured to fit into a conventional light socket.
In accordance with a further aspect of the present technique, there is provided a method of operating a lamp comprising: adjusting the switching frequency of a resonant control circuit to produce an ac signal having an adjusted switching frequency, wherein the resonant control circuit includes a variable resistor coupled in parallel with a resonant control inductor in the resonant control circuit; and applying the signal having an adjusted switching frequency to a resonant load circuit, wherein the resonant load circuit comprises a lamp.
In accordance with still another aspect of the present technique, there is provided a system comprising: a means for adjusting the switching frequency of a resonant control circuit to produce an ac signal having an adjusted switching frequency, wherein the resonant control circuit includes a variable resistor coupled in parallel with a resonant control inductor in the resonant control circuit; and a means for applying the signal having an adjusted switching frequency to a resonant load circuit, wherein the resonant load circuit comprises a lamp.
In accordance with yet another aspect of the present technique, there is provided a method of manufacturing a ballast circuit comprising: providing a resonant control circuit having a variable resistor configured to adjust the switching frequency of the resonant control circuit; and providing a resonant load circuit configured to receive an ac signal from the resonant control circuit, wherein the ac signal has an adjusted switching frequency, and further configured to control the lumen output of a lamp in response to the ac signal.
In accordance with still another aspect of the present technique, there is provided a lamp comprising: a gas discharge lamp; a ballast circuit couple to the gas discharge lamp; an input device coupled to the ballast circuit and configured to control a lumen output of the lamp; and a stem configured to couple the ballast circuit to a power supply.